The present invention relates generally to methods and means for checking or controlling the presence of oil in the air gap of electric motors and, more particularly, to improved rotors for such motors and methods of making the same.
The present invention is of particular utility in the context of hermetic compressors utilized for refrigeration purposes; and is exemplified herein in the context of a compressor wherein the motor shaft axis is horizontally disposed. It should be noted however that the benefits of the present invention may be enjoyed in other applications, including vertical motor shaft applications. It thus should be understood, as the following description proceeds, that the disclosure herein is by way of illustration and exemplification rather than for purposes of limitation.
One of the long-standing problems in the hermetically sealed refrigeration compressor art has to do with controlling the temperature of the electric motor utilized for driving the compressor. It has long been recognized that it is desirable to pump lubricating oil onto the motor for cooling purposes. For example, Mount U.S. Pat. No. 3,618,337 (which issued Nov. 9, 1971) illustrates, in a vertical motor compressor application, the concept of pumping oil from a sump to the motor winding end turns. This patent also illustrates the procedure of deliberately dispersing oil and refrigerant into the air gap between the rotor and stator of the motor. U.S. Pat. No. 3,645,112 of Mount et al (issued Feb. 29, 1972) illustrates a horizontally disposed compressor motor and, again, discloses means for deliberately dispersing refrigerant on a motor for cooling purposes. This patent also clearly shows an arrangement for deliberately moving the cooling medium (which presumably includes lubricating oil) along the air gap of the stator and rotor in the compressor.
U.S. Pat. No. 3,586,456 to Giacosa (of June 22, 1971) shows another horizontally disposed motor having a specific means for lubricating the motor bearings in a refrigerant compressor; while U.S. Pat. No. 3,600,111 to Rogers which issued Aug. 17, 1971 (and which is assigned to the same assignee as this application) shows yet another refrigeration compressor wherein the motor is horizontally disposed and wherein lubricant is transmitted to the motor for cooling purposes.
In a commercial approach widely followed by the assignee of this application, an oil tube is disposed above the magnetic core of a horizontally disposed motor, and oil dispersed therefrom showers down on the motor for cooling purposes.
We have determined that with arrangements such as those shown in the Rogers patent and such as the commercial approach just mentioned, some of the oil gets into the air gap between the rotor and stator of the motor. Moreover, whether the oil gets into the air gap inadvertently or as the result of a deliberate design, a viscous drag is applied to the rotor and the efficiency of the system is reduced.
Accordingly, it would be desirable to provide new and improved methods of operation wherein efficiency reductions associated with oil in the air gap of a hermetically sealed electric motor can be reduced, if not eliminated.
It also would be desirable to provide new and improved motor component designs, as well as methods of making the same, which would overcome the oil in air gap problem.